Optical properties of black silicon prepared by wet etching

In this paper, the optical properties of black silicon have been studied. The black silicon samples were fabricated by alkaline etching and metal assisted etching. The micro-columns and nanopores on the silicon surface were obtained in KOH and Au-induced HF/H₂O₂ solution, respectively. The height and diameter of micro-columns prepared by KOH etching is about 470 nm and 2 μm. In the Au-induced HF/H₂O₂ etching, the metallic nuclei behave as a cathode and their surrounding area acts as an anode, resulting in nanopores with diameters ranging from 80 to 120 nm. These microstructures formed in the etching process directly affect the optical properties of black silicon such as reflectance, transmittance and absorptance. According to the measurement of integrating sphere detector, the absorptance of the black silicon produced by wet etching remains roughly 90% from 250 to 1,000 nm wavelength, which is almost 150% of the absorptance of conventional silicon. However, the reflectance of black silicon is less than 13% and the transmittance is less than 4%.